It is well known that a vacuum acts as a barrier to heat flow, and hence,certain insulating materials have included a vacuum or partial vacuum to increase their heat insulating effect. The insulating effect will depend upon the extent of the vacuum, as well as the configuration of the remainder of the structure, including the amount of continuous structural contact between the opposing surfaces, because such structural contact will result in heat conduction between the surfaces.
An example of a partially evacuated multi-layer article of insulation is shown in U.S. Pat. No. 1,780,739 to Berg. Other multi-layer articles consist of thin layers of metal foil which are separated by low conductance spacers, all of which are in a vacuum. However, such articles which do include a vacuum, particularly multi-layer embodiments, are typically used only for special purpose installations, such as in cryogenic applications, due to the high cost and difficulty of manufacture of such materials. Prior to applicant's invention, to the best of applicant's knowledge, there were not any vacuum insulation articles which could compete economically with other insulation materials and which could be manufactured and handled conveniently.